Communication systems that perform a telephone call, a video conference or the like via a communication network such as the Internet or a dedicated line have become popular in recent years due to a demand for reducing travel costs and time of parties. In such a communication system, depending of a function that a communication terminal is provided with, content data such as display data of conference participants, conference material or the like, or stroke data based on handwriting operations can be shared among the communication terminals.
Moreover, a method of sharing stroke data between client apparatuses via a server apparatus among electronic whiteboards connected to a communication network has been proposed (See Patent document 1).